Percussion system



Oct. l0, 1961 R. E. WILLIAMS PERCUSSION SYSTEM l INVENTOR ILP/cuna E WILL/Aus United States Per@ O icc - a,oos,sss n n PERCUSSION SYSTEM n Richard E. williams, no. Box sserairfax, vs Filed Aug. s, y195s, ser; No. 753,859

. 1 claims. (cl. s4-1.zs)

The present invention relates generally to electronic musical instruments employing photoelectric tone generators,`, and more particularly to attack and decay cir- `for such musical instruments, kwhich are arranged and adapted for providing percussive tonal effects.

The present invention is applicable particularlyk to electric organs ofy the: type employing photoelectric generawhich are selected Vto y'absorbvery rapid changes, vwhich might otherwise give rise to clicks` in the output of the system.` The condenser is connected to the grid of "a tone amplifier, to whichis also connectedan input cir-v cuit deriving from that photoelectric cellY of the `system which is subjected to tone modulated light. Both connections tothe grid `proceed via isolating resistances, so

that interaction of the two input circuits? is prevented.

tors. A- Insuch systems one or more tone wheels may be employed,- eachv tone Wheel being provided with a plurality of'recorded soundtracks, andI each track preferably pertaining to one pitch or tone of the organ. The tone rtracks arerotated withrespect to a plurality of light sources on one side, and a photoelectric cell onthe v otherl side, eachtone track modulating the light deriving y corresponding withthe energized lamps. Systems of the I general type described are well-known, per se. The

present invention concerns itself. with the introduction of percussiveefects in such organs. ln accordance with a primary feature `of thepresent invention a supplementary photoelectric cell is employed,

whichmay be preferably of the photo-voltaic or voltagegenerating type, and which is illuminated by all the lamps, or by a predetermined plurality of the lamps of the organ. If the lamps are arrayed over a considerable area, a-plurality of such photo-voltaic cells m-ay be connected in cascade, so` that signal will be generated in responseito illumination of ,any one of the lamps for which percussive effects is desired, and so that at least one of the cells will remain, unsaturated -by light, under 'all conditions of'operation, The output of thenphoto-voltaic cell (or cells)y is applied tothe input of a voltage amplifier, so arranged "that ,one Vpositive output pulse only is generated in ,response` to energization of any lamp and one j" negative pulse only, in response to deenergization of any lamp, regardless of lthe energized condition ofthe re" mainderof the lamps.. Across the output circuit ofthe `amplifier is connected in series a gaseous discharge cell, forr example, a twoelectrode neon cell andga condenser; The voltage applied onY the neon cell inV the absence of pulses is insufficient to `iire thecell, but the positive pulses are of sucient magnitude to ignite the cell',` thereby source, and charging the condenser substantially instantaneously. A negative voltage sourceis connected in series with ahigh resistance tothe junction of the condenser junction of thecondenser in .the neon cell, and vits cathy ode connected to ground, said diode ,actingas fa clamping circuit for preventing the potential of the junctionrising `above groundr level. Connected vacross the'diode isa resistanceand condenser in sexies, the constants of VThe output ofthetone; amplifier then proceeds 'via forpowerrampliier to an electro? Inant lters and an audio acoustic transducer.

Connected betweenthe junction point of the condenser and the neon cell and ground is a switch, Which1constitutes, in its closed position, a short circuit around theA condenser, preventing any change of voltage thereacross,y and in its open condition permitting control of the volt-` age across thecondenser. This switch constitutes a percussive'stop and is controlled'by means ofa stop tab, in an actual organ. i n n The vtone ampliieris, in the absence of controlpulses, subjected to'tlie voltage of the negative source, and has a 'gain' characteristic such as to'provide substantiallyvzero gain in response to that voltage applied tothe control grid. Accordingly, the `tone amplifier is normally cutoff. In response to an input pulse of positive polarity,

the voltage" across the `condenser rises rapidly toground i the potential y of the negative source. The discharge oc-` curs quite slowly, so that the gain of the amplifier is re-` potential, which increases of the amplifier rapidly n tosubstantially full gain.. On cessation of the control pulse, thek neongcell delignites, and the condenser series .therewith discharges through the high resistance to duced with corresponding slowness to` a condition of substantially zero gain. v,

The net` effect is a rapid risein gain and a slow decrease' in ygain of the tone amplifier in response to each depressionv of a key of the' organ, regardless of the'condition ofthe remaining keys, i.e., whether they areor not de,- pressed. f3 f It is,` accordingly, Aa objectof the presentr invention to provide a novelsystem for introducingirpercussivefeects in a photoelectric musicalinstrument. v -It is a further object of the invention to provide a percussion'circuit for photoelectricrgorgans whichgshall be operated'in response only to each energization` of a lamp of a' photoelectric organ, regardless` fof the fcondition of cussive system which is entirely electronic and which v. does not rely upon the use 'ofrelays or kother ymechani- `cormyecting the condenser in serieswith a positive voltage I i,

cally moving elements., v Y f l Still a further object of. the invention resides inthe provision of apereussive circuit` for a musical instrument ,which is extremely simple, requires a minimum num-ber of inexpensive parts, is positive in action, and requires noqrnaintenance..f` n' "K Agfurther object of thetinvention resides inthe pro-` vision of a' gain controllable amplifier, in which thegain of theramplier increasesfalways to the samepredetermined value, ,and deereasestfrom the same predetermined value, in sequence, and automatically, inrespons'e rtota controlfplllse vf'given polarity.` s

provide a novel system for generating av percussive `tonal envelopew in musical instruments in lresponse to a control pulse, the percussive envelope having a predetermined fixed maximum and minimumvalue. f

Still another objectfof rthe invention-is to provide ai percussive system which'shall be operated onlyv in re` spouse to pulsesr of a given polarity; andinotin response 3 to pulses of the opposite polarity, selection being accomplished by a neon cell.

It is another object of the invention to provide a percussive circuit for electronic organs in which the rate of rise and the rate of decay of a percussive tonal envelope may be independently readily controlled over a wide range of values.

The above and still further objects, features and advantages of the present` invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE l of the accompanying drawing is a schematic circuit diagram of a system according to the invention; and

FIGURE 2 illustrates certain wave forms occurring in the system.

Proceeding now more particularly to the accompanying drawing, the reference numeral 1 denotes a tone disc applicable to photoeletric organs employing selectiveiillumination of tone tracks by means of selectively energizable lamps.

The reference numeral 2 denotes a slit disc, containingv a plurality of slits, one for each tone track, which serves to guide light from an array of lamps 3 to appropriate ones of the pitch or tone tracks 4 of the pitch disc 1. The pitch disc 1 is rotated at a predetermined rate by means of a motor 5, and the light deriving from the lamps 3, and modulated by the pitch disc 1, are all collected by means of a photoelectric cell 6. The output of the photoelectric cell is applied via a lead 7 and an isolating resistance 8 to the grid 9 of a -tone amplifier stage 1?. The stage 10 comprises a triode 11, the anode 12 of which is in series with an anode load 13 and a B-lterminal 14. Thecathode 15 of the triode 11 is connected to ground via a bias circuit 16, comprising a voltage divider connected to a source of positive voltage, thus eliminating need by a by-pass condenser.

The output from the amplifier stage is taken at the anode 12, via a lead 18, and proceeds to formant filters 19, and thence to a power audio amplifier 20 and an electro-acoustic transducer 21, all in cascade.

The lamps 3 are selectively controlled lby means of key-operated switches 22, all of which are connected in parallel to a voltage source 23, which is capable of supplying the required current and voltage to the lamps 3. Accordingly, the lamps 3 will be selectively energized in accordance with the selected ones of the switches 22, depression of a key of an organ, for example, resulting in closure of a corresponding one of the switches 22.

In accordance with the present invention a supplementary photoelectric cell of the photo-voltaic or voltagegenerating type is provided, which is identified by the reference numeral 30. This cell is so positioned with respect to the lamps that it may be illuminated by all of the lamps 3 of the array, and if this proves to be difficult or impossible at any given case, or if it leads to saturation of the cell in some conditions of operation, a plurality of similar suitably located cells may be connected in cascade. The cell 30 is connected via a bus to the grid of a triode amplifier tube 32, the grid being connected to ground via a grid leak 33 in conventional fashion. It is important to note that no differentiation takes place, because no coupling condenser is employed. The triode 32 is anode-loaded by means of a resistance 34 and is supplied with anode voltage from a B-lterminal 35, in conventional fashion. The anode of the triode 32 is coupled via a coupling condenser 36 and a grid leak 37, constituting a differentiating network, to a grid of a further triode 38, which is in turn anode-loaded by an anode resistance 39 and supplied with anode Voltage from the B| terminal 35. In response to rise of a pulse generated by the photoelectric cell 30, a positive pulse appears at the anode of the triode 38. This occurs whenever one .of the. lamps' 3 is, energized, and in response to the transient increase in illumination which occurs on such energization. Once the lamp has been energized, the output of the photoelectric cell 30 becomes a steady voltage, which is not transferred to the triode 38 because of the presence of the series coupling condenser 36.

It follows that in response to and concurrent with depression of any key of the-electronic organ, a corresponding one of the switches 22 is closed, a corresponding one of the lamps 3 is energized, and a pulse of positive polarity appears at the anode of the triode 38. When the key is released, on the contrary, only a negative pulse appears at `the anode of the triode 38, and while the key remains depressed, no change in Voltage is detectable at this anode, from the no signal condition.

The anode of the triode 38 is connected via a neon cell 40 and a large condenser 41 back to ground at its cathode. The neon cell 40 and the voltages available thereto are so selected that steady voltage at the anode of the triode 38 is not sufficient to fire the neon cell 40. It follows that negative pulses at the anode of the triode 38 have no effect, but the circuitry is so arranged that positive pulses are sufficient to fire or ignite the neon cell 40, in effect closing the circuit for the condenser 41 and charging same toward the voltage of the anode 38. Connected across the condenser 41 is a diode 44, the cathode of which is grounded. It follows that the ungrounded terminal of the condenser 41 can never rise higher than ground potential, even when the neon cell 40 is ignited, the diode 43 constituting a clamping device.

Between the junction 43 of the neon cell 40 and the condenser 41 is connected an extremely high resistance 45, which is in turn connected in series with a negative` voltage terminal 46. The diode 44 presents no conductive path to ground for a negative voltage at the terminal 46. Accordingly, the normal condition of charge for the condenser 41 is that the ungrounded terminal of the condenser 41, i.e., the junction point 43, is at the negative voltage of the terminal 46. When the neon cell conducts, a high positive voltage is applied to the terminal 43, which in effect discharges the condenser 41, bringing the ungrounded terminal to ground potential, but being incapable of raising the potential of the ungrounded potential of the condenser 41 above ground because of the clamping diode 44. The anode of the diode 44 is connetced to ground through a relatively high resistance 47 and a condenser 48, in series. The junction of the resistance 47 and the condenser 48 is connected vla an isolating resistance 49 to the grid 9 of the triode 11. The grid 9 of triode 11 is, accordingly, continually maintained at the voltage of the terminal 46, until such time as the neon cell 40 fires, raising the terminal 43 to.

ground potential, and correspondingly raising the potential of the grid 9 to ground potential. For ground potential condition of the triode 11, it has normal gain. When subjected to the negative voltage of the terminal 46, the amplifier stage 10 is inoperative, or at least operativ-e at sufficiently low gain substantially to prevent amplification of tone signals applied to the stage 10 via.

the lead 7.

The switch 50 serves to short or open the condenser 48, according as the switch 50 is closed or opened. When closed, the percussive system is disabled, resistance 49 then constituting a grid bias resistance.

The anode of the triode 11 is coupled back to the ungrounded terminal of capacitor 48 via a series connected capacitor C and resistance R. These elements, together with condenser 48 provide a low frequency degenerative feedback path for the triode 11, when the` system is percussive, which is eliminated under normal conditions, i.e., when switch 50 is closed. This feedback.

greatly -reduces low frequency thump during percussion,

and in addition the condenser C provides a Miller run-` down, increasing the capacity of the timing circuit for a given value of condenser 48.

The present system employs a single RC coupling circuit the PE. cell 30 and the trigger tube 4l), Le., the triode 32 is directly coupled to the P E. cell 30, and the triode 38-isRC coupled to the triode 3,2, no coupling condenser being required between P.E. cell `30 andtnode 32. VThis presents an unobvious advantage, eliminating any necessity for flip-fiop circuits for assurmg thatpercussive effects will occur on depressing a key only, and not onreleasing a key.

The output of the P E. cell, in response to depression and raising of akey, is essentially a square wave, 60, as at FIGUREZ, which is reversed in phaseby triode 38. The single RC coupling circuit, comprised of capacitor 36l and resistance 37, is essentially a differentiating circult, generating a negative pulse 61 at the initiation of the phase reversed square wave 62 anda positive pulse 63 atthe rise of the phase reversed square wavef62. The triode 38 introduces a further phase reversal, geni erating pulses 64 and 65 (lined of FIGURE 2)." The trigger tube fires `in response to pulse 64 and not in response to pulse 65, and in response to firing of trigger tube 46 a percussive wave form is generated. Where two RC cascaded coupling circuits employed, `as for example by providing a coupling capacitor in series with bus 3l, both the rise and the lfall of pulse 60 would give rise to 1a pair of pulses of successively opposite polarities, as 66, 67, and 68, 69. The trigger tube 40 would accordingly fire in response to both the rise and the fall of the pulse 60.

Reviewing now the operation of the present system, as the keys of an electronic organ incorporating the system are manipulated, various ones of the switches 22 are selectively closed. AClosure of any one .of the switches 22 results in illumination of the corresponding one of the lamps 3, the light from which passes through the modulating pitch disc 1 to the photoelectric cell 6, resulting in generation of tonal signal which is applied to the tonal amplifier stage for further processing in the formant filters 19 and eventual amplification by means of the audio amplifier to a suficient level for radiation as sound. The tonal amplifier stage 10 is, however, normally maintained inoperative or at sufficiently low gain that transfer-of signal therefrom does not occur, by reason of the application to the grid 9 of the stage 10 of a negative voltage deriving from the terminal 46. Whenever one of the lamps 3 is energized, a positive signal is generated at the outputtofthe photovoltaic cell 30, which is amplified by the cascaded triode tubes 36 and 38, but differentiated only once by RC circuits 36, 37, and appears at the anode of the tube 38 yas a single high positive pulse. This high positive pulse fires the' normally de-ignited neon cell 40, 'permitting passage of'current into the condenser 41. The condenser 4l is normally maintained with its ungrounded ter-r minal at a negative voltage deriving from the terminal 46. When the neon cell 40 ignites, the voltage of the ungrounded terminal condenser 41 rises to ground -potential, being prevented from rising farther by the clamping diode 44. The resistance Y47 and the condenser 48, in series, constitute a click filter, whichprevents extremely rapid application of voltage rise to the grid 9 of the triode 11. The rise time is made sufficiently slow that audible clicks are avoided. When the pulse available at the anode of the triode 38 has terminated, because the illumination from the array of lamps 3 has attained a steady state, the condenser-41 proceeds to vary its charge so that its ungrounded terminal may reattain the voltage of the terminal 46. This is a relatively slow process since the discharge must take place through the high resistance 45. Accordingly, there is generated a percussive tonal envelope which has a relatively rapid rise and a relatively slow' decay. The rise time may be adjusted byadjusting the resistance 47, while the decay time maybe adjusted by varying the value of the resistance 45.

Raising a previously depressed one of keys 22 has no effect on the percussive effect generating system, since onlyy a negative pulse is thereby generated-at the oftriode32.f The `functionof` the present system, in a vgeneral sense, is then to effect percussiver translation ofj'tones from the tone `generator of a photoelectric'organ; by generating a rapidly rising AVC voltage iny response yto and concurrent with actuation, of any key, followedby a relatively slow decay of gain, yto a no-gain condition, in the ensuing time.-`

In response to closure of any key, all the keys concurrently depressedgive rise to tones -having percussive effects -whichare cao-extensive with the; percussive effect allocable to the last depressed key. f -i The entirepercussion circuit may be readily disabled by means of a stop switch 50, which shorts out condenser 48 when closed.

While I have describedand illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing' from the' true spirit and scope of the invention as defined in the appended claims.

kWhat is claimed is:

` l. In combination, a gaseous conduction device and a condenser connected in a series circuit, means normally maintaining a voltage across said gaseous discharge device and said condenser in series which is lower than ignition voltage 4for .said gaseous conduction devices a source of negative voltage, a high resistance, means connecting said source of negative voltage via said high resistance to the junction of said gaseous conduction device and said condenser, a diode connected from the said junction to a point of reference potential in conductive direction, and means for ksupplying pulses in series with said series circuit which are of magnitude suiciently great to effect discharge of said gaseous discharge device.

2. Ina pulse formingsystem, a condenser having al first terminal and a second terminal, said second terminal being connected to a point of reference potential, a gaseous conduction device, .a source of positive pulses, said gaseous conduction device having a first electrode connected directly to said first terminal and a rsecond electrodeconnected directly to said source of positive pulses, a diode having an anode and a cathode, means connectingsaid anode to` said first terminal and said cathode to said point of reference potential, a high resistance, a source of negative voltage connected to said first terminal via said high resistance, and a pulse output circuit connected to said first terminal.

3. In a pulse forming circuit, a condenser having a first terminal and having a second terminal connected to a point of reference potential, a diode having an anode connected to said first terminal and a cathode connected to said point of reference potential, a high resistance, a

source of `negative voltage connected via said high ret sistance to said first terminal, an output lead connected to said first terminal, and means for applying positive voltage pulses to said first terminal. 4. The combination according to claim 3, wherein i further provided a switch connected for selectively interconnecting said terminals via a resistive` path. 5. The combination kiu accordance with claim 2, wherein is further provided anamplifer and an electro-acoustc transducer in cascade with said amplifier, said amplifier having signal input terminal for application of electronic tone ysignals and an automatic gain control circuit, and means for connecting said output lead to said automatic gain control circuit, said automatic gain control circuit being arranged and adapted for reducing` the gain of said amplifier in response. to voltage negative with respect toy 'F responsive to energization of any one of saidlamps under` any condition of energizatiou of the other lamps. of'sad array for gener-ating one of said positive voltage pulses. '17.1 The combination according toclaim 6, wherein said'` last means includes at least one photoelectric cell ex- 5v posed to said array of lamps.

References Cited in the file of this patent UNITED STATES PATENTSv 2,033,232 Eremeeir Mar. 1o, 1936 10 2,245,808 Oliver .lune 17, 1941 2,401,372 Rienstra June 4, 1946 2,425,600 Coykendall Aug. 12, 1947 8 2,429,775 Serght Oct. 2,8. 194.7` 2,480,599 Oxford Aug. 30,Y 1949 2,776,422 Slusser j Ian. 1,19-57 2,796,534 Williams v lune 18, 1957y 2,823,310 Anderson Feb. 11, 19,5 8`

OTHER .REFERENCES Bell: published application Serial No. 558,041, published Oct. 1l, 1949; 627 O G. 576i.

Douglas: Percussion Circuits for Electronic Musical instruments, Electronic Engineering, July 1958, pp. 420 lto 423. 

